One of the most acclaimed films of the 90's was REAL and quite possibly the front runner for the best documentary ever. The biggest snub in Oscar history, etc.
It starts out in the 1980's following two 14 year old naturals from the projects of Chicago as they're headhunted by talent scouts, lured in by schools, their offers of subsidised education and the shot at living their dream of NBA stardom.
Initially the two were uninteresting and thin, but 15 minutes in, once they get to the school stages they realize that fulfilling their dreams is going to be a mountain to climb with pressure bearing down on them from all directions; Coaches with nothing positive to say, criticism from family members, unexpected hikes in tuition fees, parents losing their jobs, families breaking up, unexpected pregnancies. The beauty of the film is that it avoid your typical Documentary pitfalls of some generic talking head in a suit popping up for 30 seconds, prattling on about a subject, only being identified by title at the bottom of the screen before never being seen again. Once the film gets going, it becomes more than just the lives of 2 people, everyone of note gets fleshed out and becomes more watchable than most actors will be in their entire careers. No reconstructions, pretty much every moment of importance is captured on film minus an impregnation here and there.
Those put off by the 3 hour run time shouldn't be, it only gets deeper deeper with each passing minute so you're never left thinking 'eh, it's dying off a bit now'. Quite easily the best documentary I've ever witnessed and I've seen some good ones (Grizzly Man, Deliver Us From Evil, Koyaanisqatsi, 102 Minutes That Changed America, the overrated Man On Wire).
Simply put Hoop Dreams is #1.